<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        /* 简写形式和padding一样 */
        .first{
            width: 200px;
            height: 200px;
            margin-bottom: 20px;
            background-color: skyblue;
        }
        div{
            width: 200px;
            height: 200px;
            background-color: slateblue;
        }
    </style>
</head>
<body>
    <div class="first"></div>
    <div></div>
    <div></div>
    <div></div>
</body>
</html>